<!doctype html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>下拉框</title>
	<script type="text/javascript">
		window.onload=function(){
			father=document.getElementById('father');
		son=document.getElementById('son');
		father.onmouseover=function(){
			son.style.display="block";
			
		}
		father.onmouseleave=function(){
			son.style.display="none";
		}
		}
	</script>
	<style type="text/css">
		#father{
			width: 200px;
			height: 60px;
			background-color: gray;
			position: relative;
		}
		#son{
			width: 200px;
			height: 200px;
			background-color: red;
			position: absolute;
			top: 60px;
			left: 0px;
			display: none;
		}
	</style>
</head>
<body>
	<div id="father">
		<div id="son"></div>
	</div>
</body>
</html>